Moving people on a possibly poorly lit stage using a short lens and being a long distance away is going to make it very difficult to get any good images regardless of settings.

First thing is to get closer to the action so that you can use that short lens properly. There's a reason sports photographers use long lenses.

Secondly set the ISO as high as possible to get the best light.

Then use the camera on P, A, or S mode. Attempting to get the right exposure on M mode, if you're not practiced, will take so long that you'll miss all the action.

If you can use a flash to get extra light on the subject. If the D5100 has a rear curtain flash sync setting then use that with P mode to get images with some motion blur but still give you bright subjects.

With a D100 + external flash in M mode under similar conditions I'd use ISO 400, 1/125 for flash sync, lowest F stop available and manually dial in the flash power to 1/8 to 1/4 or even 1/2 depending on conditions and distance - but that's from a lot of experience taking photos at concerts and in clubs.